# what is feedback in the circuit?

Discussion in 'The Projects Forum' started by vivek20055, Nov 8, 2012.

1. ### vivek20055 Thread Starter Member

Nov 4, 2012
88
0
Hello,

I am new to electronic circuits. Can anyone tell me what is feedback in the circuit?

Thanks & regards,
Vivek Alaparthi

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2. ### xainnasir New Member

Nov 8, 2012
26
2
feedback is usually a sensor which is getting the input from the system's output and after making a comparison it gives the output which is then compared with the system input .... this sensor's output is called feedback

3. ### wmodavis Well-Known Member

Oct 23, 2010
737
150
Feedback means some of the output from the circuit is added back into the input of that same circuit. If the fed back signal is in phase with the input signal it will reinforce it and possible cause oscillation (that is what makes an oscillator work). If the output signal is fed back to the input out of phase it has the opposite effect but has many advantages. Some are: reducing distortion, adding stability and increasing frequency response.

So in the circuit you show look for instance where the output of the various circuit elements is connected back to its input using come feedback controlling component like a resistor or capacitor. I'll let you look for that.

4. ### vivek20055 Thread Starter Member

Nov 4, 2012
88
0
Hello,

I think D2 and D3 are feedback elements and that loop is feedback loop in the circuit. Is it correct?. If not what is the answer.

Thanks & regards,
Vivek Alaparthi

Apr 30, 2011
1,425
363
I see no D2 here.

6. ### vivek20055 Thread Starter Member

Nov 4, 2012
88
0
Hello,

I mean D1 and D3 in the circuit

Thanks & regards,
Vivek Alaparthi

7. ### tubeguy Well-Known Member

Nov 3, 2012
1,157
197
D1 and D3 are providing feedback.
When Q3 is "on" it will lower the voltage on the + input of U2 thru diode D1.
When Q4 is on - same with U1 and D3.
Curious, what type of AND gate is used?

8. ### ScottWang Moderator

Aug 23, 2012
4,850
767
There are two problems in the input(+) of Op amp, you can't force the output of AND gate to 0.7V through diode when the output is high(+5V).

There are two ways to solve the problems:
1) series two 100Ω resistors into the output of AND gate.
2) Choose 74HC09 OD AND gate.

The better way is to use 74HC09.

74HC09 datasheet, two input AND gate(Open Drain).
http://www.datasheetcatalog.org/datasheet2/c/0ggx27i2eq1g0rp5up3e2c3hsawy.pdf

• ###### Detector_OpAmp.gif
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Last edited: Nov 8, 2012
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9. ### vivek20055 Thread Starter Member

Nov 4, 2012
88
0
Hi,

How to know where I need to use resistor in a circuit?. On what basis, I need to calculate the resistor values. Is ohms law is the only method or any other method is there?

Thanks & regards,
Vivek Alaparthi

10. ### vivek20055 Thread Starter Member

Nov 4, 2012
88
0
Hello,

I do not understand, why these spikes in AND gate output as shown in figure. The AND gate output is just 5V pulse and the MOSFET needs 10 to 12v pulse to ON/OFF.
But this circuit is working. The gate driver output is 10v. Is the gate driver is having pull up voltage capacity?.

Vivek Alaparthi

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11. ### ScottWang Moderator

Aug 23, 2012
4,850
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Please see the #8 again, and do as those.

After doing as above, and doing the next test.
Take off the diode 4004, and measure the output of AND gate.

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12. ### vivek20055 Thread Starter Member

Nov 4, 2012
88
0
Hello,

Yes, I think it is better to use the AND gate model 74HC09 OD. But where can I get the pspice simulation model for the AND gate 74HC09 OD. My simulation tool is not having the AND gate 74HC09 OD.

Thanks & regards,
Vivek Alaparthi

Aug 23, 2012
4,850
767
14. ### vivek20055 Thread Starter Member

Nov 4, 2012
88
0
Hi,

I need to eliminate the ripples in the output current of the coil in the circuit.

Can anyone suggest me, how to eliminate the ripples in the current?